Control And Regulation Of Maternal Behavior

Species-specific maternal behavior appears spontaneously after delivery, even in naive animals. Prior to birth many females are indifferent, or even aggressive, to neonates, but maternal behavior is expressed immediately at the birth of their own young. The rapid onset of maternal care requires hormonal priming by an increase in ovarian hormones (estrogen and progesterone) and

Fig. 3 Schematic diagram of the neuroendocrine events occurring during pregnancy and at birth that lead to the onset of maternal behavior in mammals. (Derived from data given in Ref. [2].) (View this art in color at www.dekker.com.)

particularly by the substantial changes in the relative concentrations of these hormones that precedes birth. This priming functions to prepare the maternal brain by increasing oxytocin receptors in key brain regions. At birth, neural impulses travel up through the spinal cord when the birth canal stretches by the passage of the foetus (the Ferguson Reflex) and these impulses stimulate the release of oxytocin in the brain and into the periphery (Fig. 3). This acts as a trigger for the expression of the suite of maternal behaviors.[2] For example, in the sheep it causes maternal licking of the newborn lamb and many low-pitched bleats or ''rumbles'' (a specific vocalization made by ewes to their lambs). Other chemicals (e.g., opioids, glucocorticoids) act as modulators of maternal behavior expression.

In many species, females that are maternal for the first time (primiparas) often show poorer expression of maternal behavior, and mortality of offspring of these mothers is higher than with experienced dams. For most species, the act of giving birth and showing maternal care causes a maturation of the hormonal processes described above.[3] In some species, such as primates, young females can gain experience of maternal behavior through allomothering, where they share in the care of their younger siblings or the offspring of their older siblings.

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